Laser techniques for welding soft tissue have been in development for about thirty years. See, for example, "Biological Effects of Laser Welding on Vascular Healing," by Rodney A. White et al., Lasers in Surgery and Medicine 6, 137 (1986). The general procedure is to utilize a laser to locally sufficiently heat the tissue to be welded at the site of a surgical closure, such that the tertiary structure of bonding proteins occurs without significant chemical damage thereto. In "Heat-Free Photochemical Tissue Welding With 1,8-naphthalimide Dyes Using Visible (420 nm) Light," by M. M. Judy et al., SPIE 1876, 175 (1993), the authors synthesized a class of photochemical dyes which function as photoalkylation agents following activation with visible light. The activated species react readily with nucleophilic amino acid residues, and have been used to bond collagenous dura mater sheets to each other with weld shear strengths of up to 425 g/cm.sup.2. Moreover, in "Reinforcement Of Cholonic Anastomoses With A Laser And Dye-Enhanced Fibrinogen," by Nader Moazami et al., Arch. Surg. 125, 1452 (1990), the authors applied indocyanine green dye-enhanced fibrinogen to the serosal surface of two-layer inverting anastomoses, and exposed the surfaces so treated to 808-Nm diode laser radiation. The characteristic drying of the glue to a light brown, and the loss of glistening of the fibrin, indicated the end point. Bursting pressures of the sutured anastomoses without the fibrin glue were significantly less than those anastomoses reinforced with the fibrin glue. The laser-fibrinogen-reinforced suture anastomoses do not require such precise apposition as an anastomosis primarily made by laser. The dye-enhanced fibrinogen absorbs most of the laser energy and thus prevents excessive heating of the substrate tissues. The authors conclude that prevention of anastomotic leakage during the critical first week following surgery should significantly reduce complications associated with such procedures. In "Dye-Enhanced Laser Tissue Welding," by Roy S. Chuck et al., Lasers in Surgery and Medicine 9, 471 (1989), the authors describe the use of a saline solution of fluorescein isothiocyanate in order to reduce the cw argon ion laser energy required for welding, thereby minimizing thermal damage to surrounding, healthy tissue. This concept is supported by Mehmet C. Oz et al. in "Indocyanine Green Dye Enhanced Vascular Welding With the Near Infrared Diode Laser," Vascular Surgery 24, 564 (1990), who state that the minimal injury to tissue within and surrounding the weld may allow more rapid proliferation of myofibroblasts and the deposition of extracellular matrix necessary for regeneration of the vascular tissue at the weld site. Moreover, the authors observe that the 808 nm output of the diode laser is very poorly absorbed by soft tissue. However, this frequency matches the absorption of indocyanine green, and the laser/dye combination can cause substantial and rapid tissue effects.
Although the mechanisms involved in tissue welding are poorly understood, in "Changes In Type I Collagen Following Laser Welding," by Lawrence S. Bass et al., Lasers In Surgery and Medicine, 12, 500 (1992), the authors believe that as a result of absorption of laser light, structural changes occur in the extracellular matrix proteins. They conclude that non-covalent interactions between denatured collagen molecules produced thereby may be responsible for the creation of tissue welding. Irradiation was performed without smoking or charring. In "Laser-Induced Alteration of Collagen Substructure Allows Microsurgical Tissue Welding," by R. Schober et al., Science 232, 1421 (1986), the authors report that histological and fine structural analysis revealed a homogeneous change in collagen with interdigitation of altered individual fibrils as the apparent structural basis of the welding effect.
To date, however, there has been no successful laser welding of hard tissues. The mineral component has greatly different thermal properties than Type I collagen, and likely hinders the welding mechanism thought to be caused by collagen.
Accordingly it is an object of the present invention to provide a method for welding bones using electromagnetic radiation.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.